Patent GB-1404923-A (GB)
Title: Brake control apparatus
IPC: B60T13/66
Filed: 1974-01-14
Abstract: 1404923 Automatic control of pressure A M YARBER 14 Jan 1974 01683/74 Heading G3R [Also in Division F2]  A pressure regulating valve 80 is operable to supply (hydraulic or pneumatic) fluid output pressure to a vehicle wheel brake 65 in response to electrical signals from logic circuitry 68 which signals control the operation of solenoid pilot valves 100, 110; the logic circuitry 68 is itself operable in response to a difference signal S3 which represents the difference between an electrical command signal S6 and a monitor signal S2 produced by a transducer mechanism 50 and said to be representative of the value of the output pressure of the valve 80. Should the signal S3 deviate from a normal equilibrium value the logic circuitry 68 causes operation of the pilot valves 100, 110 to control the valve 80 to alter the output pressure in a manner to bring the signal S3 back to its normal equilibrium value. As shown, a poppet member 82 of the valve 80 controls fluid-flow between an output chamber 74, a pressure chamber 76, and a return chamber 78 - the output chamber 74 is connected to wheel brake 65 and pressure and return chambers 76, 78 are connected to suitable pressure sources, shown as the pressure and suction sides of the pump 72. Poppet member 82 has a through bore 81 and forms an inlet valve 84 which controls pressure flow from chamber 76 to output chamber 74 and in co-operation with a valve plate 86 an outlet valve 88 which controls flow from outlet chamber 74 via poppet bore 81 to return chamber 78. Pressure regulating valve 80 acts to maintain in chamber 74 a pressure proportional to the control force applied via a valve actuating plunger 90. The plunger 90 is biased by the force of a spring 92 towards valve plate 86 which force varies with the position of a piston 94 movable in a chamber 96 in response to fluid-pressures acting on its two opposite faces. The pressure in a feedback chamber 96a of chamber 96 is maintained equal to the output pressure in chamber 74 by a passage 98 while the pressure in control chamber 96b of chamber 96 is caused to vary by means of pilot valves 100, 110. Valve 100 is open in its de-energized condition and controls flow from chamber 76 to chamber 96b and valve 110 is closed in its de-energized condition and controls flow from chamber 96b to chamber 78. The plunger 90 slides in a bore in piston 94 and forms a chamber 97 connected to return chamber 78. The circuitry controlling operation of the pilot valves 100, 110 comprises a line 12 in which a command signal S 1 is developed by a potentiometer R1 controlled by a handle 13. This signal S 1 may be modified by an anti-skid signal S5 - a potentiometer R2 driven by a mechanism 62 under the control of braked wheel 64 provides a signal which becomes increasingly positive as the wheel decelerates and the skid signal is amplified and inverted to provide negative signal S5. The signal S5 is summed with command signal S to give the final command signal S6 at junction A, which is then compared with the monitor signal S2 derived from the transducer mechanism 50. This mechanism 50 comprises a potentiometer R10 coupled by a rod 52 to the piston.94 so that the signal on line 58 varies with the position of piston 94 and is said to be proportional to the output pressure produced by valve 80. To ensure prompt response of difference signal S3 to changes in monitor signal S2 the initial monitor signal on line 58 is differentiated by a capacitor C2, amplified by an amplifier M4 and the resulting signal is summed with difference signal S3 in such polarity as to steepen the rate of change of the latter signal in response to a change of monitor signal S2. As illustrated, the differential signal is coupled to a line 67 by a capacitor C3, but signal summation may take place at junction B. The signal S3 is applied to NPN switching transistors Tr1, Tr2 which via PNP power transistors Tr3, Tr4 control the solenoids 102, 112 of valve 100, 110. With S3 negative with respect to its equilibrium value which may be ground potential valve 100 is open and valve 110 is closed to raise the output pressure; with S3 zero both valves 100, 110 are closed to hold the brake pressure; with S3 positive valve 100 is closed and valve 110 is open to lower the output pressure.